Quinine, a natural product, was investigated as a corrosion inhibitor for low carbon steel in 1.0 M HCl solution. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study the inhibition action in the temperature range 20-50 degrees C. The corrosion of steel was controlled by a charge transfer process at the prevailing conditions. The electrochemical results showed that quinine is an efficient inhibitor for low carbon steel and an efficiency up to 96% was obtained at 20 degrees C. The inhibition efficiency increases with inhibitor concentration and reaches a near constant value in the concentration range 0.48 mM and above. Application of the Langmuir adsorption isotherm enabled a study of the extent and the mode of adsorption.